Given:
- The ratio of copper to zinc in the alloy is 2:11.
- The weight of zinc in the alloy is 28.6 grams.

To Find:
- The weight of copper in the alloy.

Solution:
Step 1: Calculate the total ratio of copper and zinc in the alloy.
- The total ratio of copper and zinc is 2 + 11 = 13.

Step 2: Calculate the weight of copper in the alloy.
- To find the weight of copper, we need to calculate the fraction of copper in the alloy.
- The fraction of copper can be calculated as (weight of copper)/(total weight of the alloy).
- Since the weight of zinc is given, we can calculate the weight of copper using the fraction of copper.
- Let's assume the weight of copper in the alloy is 'x' grams.
- The weight of zinc in the alloy is 28.6 grams.
- The weight of the alloy is the sum of the weight of copper and the weight of zinc, so the total weight of the alloy is x + 28.6 grams.
- The fraction of copper is x/(x + 28.6).
- According to the given ratio, the fraction of copper should be 2/13.
- So, we can set up the equation as x/(x + 28.6) = 2/13 and solve for x.

Step 3: Solve the equation to find the weight of copper.
- Cross multiplying the equation, we get 13x = 2(x + 28.6)
- Solving for x, we get 13x = 2x + 57.2
- Subtracting 2x from both sides of the equation, we get 11x = 57.2
- Dividing both sides of the equation by 11, we get x = 57.2/11
- Simplifying, we get x ≈ 5.2 grams.

Step 4: Conclusion
- The weight of copper in the alloy is approximately 5.2 grams.